We have two types of climatic classifications, that is the Greek System of climatic classification and Koppen’s scheme. Both have their functions according to how they are used, we are going to look at this classification of climates one by one and also discuss how Greek System and Koppen’s scheme work together.
The Greek System: The Greeks were among the first set of people in the world to classify climates. Their scheme divided the world into the following three climatic zones based on temperature:
1. Torrid or Hot: Areas within the Tropics that experience intense heat.
2. Frigid or Very Cold: Areas of excessive cold in the Arctic and Antarctic regions.
3. Temperate or Mild: Areas lying between the torrid and frigid zones which are neither too hot nor too cold.
The Greek scheme is inadequate because:
1. It is simplistic.
2. It ignores such vital climatic factors as latitude, altitude, prevailing winds, vegetative cover, and ocean currents.
Koppen’s Scheme: Koppen’s scheme has five major groups which have been coded alphabetically:
A – Tropical rainy climates, with no month cooler than 18 degrees.
B – Dry climates, in which potential evaporation exceeds annual precipitation.
C – Warm temperate rainy or Humid Mesothermal climates, with the coldest month below 18 degrees, but above – 3 degrees.
D – Cool temperate or Microthermal climates, with the coldest month below – 3 degrees, and warmest month above 10 degrees.
E – Polar or ice climates, with the warmest month below 10 degrees.
Koppen went further to add secondary letters to the above letters in order to differentiate between sub-divisions within the five major groups. The secondary letters in Koppen’s scheme climate classification and what they stand for are:
f – adequate rain all months
F – ice cap, with perpetual frost
m – rain forest despite the short dry season
s – summer dry season
S – steppe, with 360 – 760mm rain in low latitudes
T – tundra
w – winter dry season
W – desert, with less than 250mm rain per year
A third letter was added later to include information about temperature thus:
a – hot summer, with the warmest month greater than 22 degree
b – warm summer, with less than 22 degree
c – cool, short summer, with only four months greater than 10 degree
d – very cold winter, with less than -38 degree
h – dry-hot, with a mean annual temperature greater than 18 degree
k – dry cold, with less than 18 degree
The above letters are grouped together and ascribed to appropriate climatic belts, e.g. BW – Hot desert climate and vegetation
BS – Steppe climate and vegetation
BWK – Cool desert climate
Dfe – Cold, snowy forest climate with cool, short summer
Merits of Koppen’s Scheme:
- It is simple.
- It is quantitative because it has used numerical values to define the boundaries of climatic groups.
- It makes it easy to ascribe a given place to a particular climate sub-group on the basis of temperature and precipitation.
Demerits of Koppen’s Scheme:
- It is inconsistent because he used mean temperature for his A, C,D, and E zones; whereas his zone B is based on precipitation – evaporation ratio.
- It is not comprehensive enough because it has not taken the case of the climates of mountainous regions and regions affected by fog.
- The boundaries of Köppen’s climate types are too strictly empirical.